1. Field of the Invention
The present invention relates to a robot control system for controlling a set of industrial robots (hereinafter referred to simply as "robots") for cooperative operation and, more specifically, to a robot control system for controlling a set of robots for cooperative operation according to a single control program.
2. Description of the Prior Art
Referring to FIG. 7, a conventional robot control system for controlling a set of four robots Ra, Rb, Rc and Rd for processing a work W comprises memories 12, 22, 32 and 44, reading/compiling units 13, 23, 33 and 43, instruction executing units 14, 24, 34 and 44, and servomechanisms 15, 25, 35 and 45, respectively, for controlling robots Ra, Rb, Rc and Rd. The reading/compiling units 13, 23, 33 and 43 are interconnected by a communication line 50 for the cooperative operation of the robots Ra, Rb, Rc and Rd.
Individual control programs for controlling the robots Ra, Rb, Rc and Rd are stored respectively in the memories 12, 22, 32 and 42. The control programs are made so that the robots Ra, Rb, Rc and Rd will not interfere with each other during operation and will operate in a predetermined sequence.
When the robots Ra, Rb, Rc and Rd are operated sequentially one at a time as shown in FIG. 8 , each of the control programs includes communication instructions, such as STOP, START and WAIT, for communication between the robots Ra, Rb, Rc and Rd in addition to an operation instruction, such as MOVE TO.
In such a conventional robot control system for controlling a plurality of robots for cooperative operation, a position is expressed in the program by a coordinate system which is individual for the corresponding robot. Therefore, it is difficult to determine respective positions of the robots relative to each other, and hence it is difficult to make programs capable of satisfactorily controlling the robots for cooperative operation and avoiding collision between the robots.
Furthermore, since the programs are made individually for the robots, it is difficult to realize the relation between the actions of the robots from the programs and hence it is difficult to find errors in the programs and to correct the programs.
FIG. 9 shows another conventional robot control system for controlling four robots Ra, Rb, Rc and Rd for cooperative operation to process a work W. The robot control system comprises a system controller 7, robot controllers 1a, 2a, 3a and 4a respectively for controlling the robots Ra, Rb, Rc and Rd, connected to the system controller 7, teaching units 1b, 2b, 3b and 4b connected respectively to the robot controllers 1a, 2a, 3a and 4a to teach the robots Ra, Rb, Rc and Rd, and a sequence program input unit 9 connected to the system controller 7 to give an actuating sequence control program to the system controller 7. Control programs are stored respectively in the memories of the robot controllers 1a, 2a, 3a and 4a to control the robots Ra, Rb, Rc and Rd for a series of operations. Also connected to and controlled by the system controller 7 are auxiliary equipment including a conveyor 6 for conveying the work W, a positioning device for positioning the work 1, chucking mechanisms, safety mechanisms, and interlocking mechanisms for avoiding interference between the robots Ra, Rb, Rc and Rd. A sequence controller 8 included in the system controller 7 controls the robots Ra, Rb, Rc and Rd and the auxiliary equipment for sequential operation.
This conventional robot control system requires the robot controllers and the teaching units individually for the plurality of robots, and must teach operating procedures individually to the plurality of robots every time the contents of process changes. The system controller provided in addition to the robot controllers increases the floor space necessary for installing the robot control system.
Furthermore, complicated wiring to interconnect the robots and the robot controllers, and the robot controllers and the system controller for controlling the robots for coordinated cooperative operation requires much time for designing and installing the wiring.
When the work is changed or modified requiring changing the robots and the auxiliary equipment, the modification of the machining system and the robot control system, and teaching new motions to the robots require much time.
FIG. 10 shows a third conventional robot control system for controlling two robots Ra and Rb for cooperative operation to process a work W. The robot control system comprises two robot controllers 4 and 5 respectively for controlling the robots Ra and Rb.
The robot controller 4 (5) comprises a memory 6 (7), an instruction compiler 8 (9), a driving unit 10 (11), and a synchronizing unit 12 (13). The synchronizing units 12 and 13 of the robot controllers 4 and 5 are interconnected by an external communication cable 14 to control the robots Ra and Rb for synchronous operation. Individual control programs for controlling the robots Ra and Rb are stored respectively in the memories 6 and 7. The control programs must be designed to control the robots Ra and Rb for predetermined sequential operation so that the robots will not interfere with each other.
In executing the control programs, contact inputs and outputs are transmitted through the external communication cable 14 between the synchronizing units 12 and 13.
Examples of the control programs for controlling the robots Ra and Rb include the following instructions.
Control Program for the Robot Ra:
MOVE TO P.sub.1
OUT #1, ON
WAIT UNTIL #2=ON
MOVE TO P.sub.3
Control Program for the Robot Rb:
WAIT UNTIL #1=ON
MOVE TO P.sub.2
OUT #2, ON
According to these instructions, the robot Rb starts to operate upon the arrival of the robot Ra at a set position P.sub.1, while the robot Ra remains in a standby state until the robot Rb arrives at a set position P.sub.2. Upon the arrival of the robot Rb at the set position P.sub.2, the robot Ra moves to a set position P.sub.3. A signal indicating the arrival of the robot Ra at the set position P.sub.1 is transmitted through a line 14a of the external communication cable 14, and a signal indicating the arrival of the robot Rb at the set position P2 is transmitted through a line 14b of the external communication cable 14.
Thus, this conventional robot control system needs the external communication cable 14 and the synchronizing units 12 and 13 for communication between the robot controllers 4 and 5 to control the robots Ra and Rb for synchronous operation. The external communication cable 14 must have an increased number of lines for specific purposes to transmit increased amount of information between the robot controllers 4 and 5. Accordingly, the robot control system is expensive, and the modification of the robot control system for adaptation to different processes is difficult.